This invention relates to a microsurgery apparatus and, more particularly, a cornea laser-cutting apparatus adapted for use in cutting out a cornea in full thickness during cornea transplant surgery or keratoplasty.
Despite advances in corneal preservation and transplantation, postoperative astigmatism remains the most important complication limiting visual acuity after penetrating keratoplasty. The major contributing factor appears to be the difficulty in creating a truly round recipient opening.
Conventionally, mechanical cutting methods have been applied to such cornea transplanting surgery or keratoplasty by means of a trepan and corneal scissors. However, these mechanical cutting methods are apt to cause strain and/or deformation on the cornea being removed, and often result in incorrect sizing of a donor cornea to a recipient opening. As a result, patients with corneas which have been transplanted from a donor's eye experience astigmatism.
In addition, a two step surgical operation is required in the conventional method using a trepan and corneal scissors so that it takes an ophthalmologist a very long time to carry out the cornea transplantation or keratoplasty.
Further, an ophthalmologist is required to learn a particularly delicate, skilled technique to cut out corneas using the prior art methods.
Current techniques of punching the donor from the endothelial side generally result in a fairly circular button. Sewing such a circular button into an oval hole, however, results in different amounts of corneal tissue along the major and minor axes of the elliptical opening, and in astigmatism. These tissue differences may be temporarily compensated for by selective suture removal. Ultimately, however, sutures loosen and must be removed. Variations in the shape of the recipient opening from patient to patient are a likely explanation for the sometimes substantially different amounts of astigmatism experienced by one surgeon using the same technique.
Noncontact trephination of the cornea, if possible, would minimize distortion and enchance the likelihood of producing a circular opening. The application of lasers which cut the cornea provide the potential for such a trephine system.
Excimer lasers have been investigated in the past to produce linear corneal incisions. The argon fluoride excimer laser emitting at 193 nm has been shown to produce sharp, smooth-walled corneal cuts. More recently, the hydrogen fluoride laser emitting at 2.9 .mu.m, which corresponds to the peak absorption wavelength of water, has been experimentally used to produce linear corneal incisions. Laser trephination, achieved by focusing the beam into a ring, has been proposed as a method for drilling large diameter holes for industrial applications. The axicon, a diverging prismatic lens, has been used for this purpose and has been studied extensively since its discovery by McLeod in 1954. An axicon system previously was used by Beckman and associates to study corneal trephination with a carbon dioxide laser. This experimentation is described in an article entitled "Limbectomies, Keratectomies, and Kerastomies Performed With a Rapid-Pulsed Carbon Dioxide Laser" in American Journal of Ophthalmology, Vol. 71, No. 6, (June 1971). In this article, Beckman et al describe the use of an axicon lens in combination with a focusing lens to form an "optical trephine" and perform various corneal experiments with animal's. The diameter of the trephine was governed by the focal length of the focusing lens in these experiments. Therefore, to vary the size of the circular beam, it was necessary to change the focusing lens in this arrangement, which in addition varied the width of the annulus. This would require a time consuming process to adjust the diameter of the trephine for each patient or donor. In addition, the optical system is more complex than that of the present invention, and requires the use of multiple focusing lenses of different focal length.